Multiple reflection layer electrode, compound semiconductor light emitting device having the same and methods of fabricating the same

ABSTRACT

Provided are a multiple reflection layer electrode, a compound semiconductor light emitting device having the same and methods of fabricating the same. The multiple reflection layer electrode may include a reflection layer on a p-type semiconductor layer, an APL (agglomeration protecting layer) on the reflection layer so as to prevent or retard agglomeration of the reflection layer, and a diffusion barrier between the reflection layer and the APL so as to retard diffusion of the APL.

PRIORITY STATEMENT

This application claims priority under 35 U.S.C. §119 to Korean PatentApplication No. 10-2006-0101576, filed on Oct. 18, 2006, in the KoreanIntellectual Property Office (KIPO), the entire contents of which areincorporated herein by reference.

BACKGROUND

1. Field

Example embodiments relate to a multiple reflection layer electrode of asemiconductor device, a compound semiconductor light emitting devicehaving the same and methods of fabricating the same. Other exampleembodiments relate to a multiple reflection layer electrode havingimproved thermal stability and ohmic contact characteristics, a compoundsemiconductor light emitting device having the same and methods offabricating the same.

2. Description of the Related Art

FIG. 1 is a cross-sectional view of a structure of a conventionalcompound semiconductor light emitting device (LED) 50 and a conventionalp-type electrode 30 formed on a p-type nitride semiconductor layer 16.FIG. 2 is a photograph showing the surface of the compound semiconductorLED on which the p-type electrode 30 is annealed, and FIG. 3 is ascanning electronic microscope (SEM) cross-sectional photo showingagglomeration of the annealed p-type electrode 30 and voids 32 formed inthe p-type electrode 30 as a result of agglomeration.

Referring to FIG. 1, the conventional semiconductor LED 50 may includean n-type nitride semiconductor layer 12, an active layer 14, and ap-type nitride semiconductor layer 16, which are sequentially formed ona sapphire substrate 10, an n-type electrode 20 formed on one side ofthe n-type nitride semiconductor layer 12, and a p-type electrode 30formed on the p-type nitride semiconductor layer 16. If forward voltagesare applied to LED electrodes, for example, the n-type electrode 20 andthe p-type electrode 30, electrons in a conduction band of the activelayer 14 may be recombined with holes in a valence band and light may beemitted from the active layer 14 due to energy corresponding to a bandgap, which is the energy difference between the valance band and theconduction band. Light emitted from the active layer 14 may be reflectedby the p-type electrode 30 and may be emitted to the outside of thesemiconductor LED 50 through the sapphire substrate 10.

In an LED in which light generated from the semiconductor LED 50 is notdirectly emitted onto the sapphire substrate 10, but is reflected by thep-type electrode 30 and emitted through the sapphire substrate 10(hereinafter, referred to as a flip-chip LED), because the p-typeelectrode 30 may reflect light, the p-type electrode 30 may be formed ofa conductive metal having increased reflectivity, e.g., Ag.

A semiconductor having a relatively large direct bandgap energy (about2.8 eV or more) may be essential for blue light emission. Semiconductordevices, which emit a blue or green light by primarily using a GroupII-VI ternary system material, have been developed. However, due to arelatively short operating time, there are problems in applyingsemiconductor devices. Recently, semiconductor devices for blue lightemission have been studied in Group III-V semiconductors. Among them,Group III nitride (for example, a compound related to GaN)semiconductors may be relatively stable to optical, electrical, andthermal stimulus and may have an increased luminous efficiency.

As illustrated in FIG. 1, in an LED that uses a Group-III nitridesemiconductor, e.g., GaN, as a semiconductor light emitting device, forimprovement in light extraction efficiency, the p-type electrode 30 maybe formed of a metal having increased reflectivity, e.g., Ag, on thep-type nitride semiconductor layer 16. In order to form the p-typeelectrode 30 on the p-type nitride semiconductor layer 16, an electrodemay be deposited on the p-type nitride semiconductor layer 16 and then,annealing may be necessary for reduction in resistance.

However, in general, a surface energy of a nitride semiconductor and asurface energy of a metal material, e.g., Ag, used in forming the p-typeelectrode 30 may be different from each other. Due to the difference insurface energies, agglomeration may occur in the p-type electrode 30during annealing, as shown in the photographs of FIGS. 2 and 3. FIG. 2is a plan-view of a captured image of the n-type electrode 20 and p-typeelectrode 30 in which surface agglomeration occurs after annealing, andFIG. 3 is an SEM cross-sectional photo of the p-type electrode 30 inwhich agglomeration occurs after annealing. As shown in FIGS. 2 and 3, aplurality of voids 32 may be formed at an interface between the p-typenitride semiconductor layer 16 and the p-type electrode 30. Whenagglomeration occurs in the p-type electrode 30, a plurality of voids 32may be formed. As a result, reflectivity of the Ag electrode 30 may belowered and an optical output of the entire LED may be reduced.

SUMMARY

Example embodiments provide a nitride-based semiconductor light emittingdevice which prevents or retards agglomeration from occurring in ap-type electrode when a semiconductor light emitting device ismanufactured, thereby suppressing the lowering of an optical output of alight emitting device (LED) using a nitride semiconductor and showingincreased brightness.

According to example embodiments, a multiple reflection layer electrodemay include a reflection layer on a p-type semiconductor layer, an APL(agglomeration protecting layer) on the reflection layer so as toprevent or retard agglomeration of the reflection layer, and a diffusionbarrier between the reflection layer and the APL so as to prevent orretard diffusion of the APL.

The multiple reflection layer electrode may further include a contactelectrode layer between the p-type semiconductor layer and thereflection layer so as to reduce a contact resistance between the p-typesemiconductor layer and the reflection layer. The contact electrodelayer may be formed of at least one material selected from the groupconsisting of a La-based alloy, an Ni-based alloy, a Zn-based alloy, aCu-based alloy, a thermoelectric oxide, a doped In oxide, ITO, and ZnO.The reflection layer may be formed of one material selected from thegroup consisting of Ag, an Ag-based alloy, and an Ag-based oxide. TheAg-based alloy may include at least one element selected from thesolute-element group consisting of Al, Rh, Cu, Pd, Ni, Ru, Ir, and Pt.

The diffusion barrier may be formed of a transparent conductivematerial. The transparent conductive material may include at least onematerial selected from the group consisting of Ti—N, Mo—O, Ru—O, Ir—O,and In—O. The In—O further may include at least one dopant selected fromthe group consisting of Sn, Zn, Ga, Cu, and Mg. A content of a dopantadded to the In—O may be about 0.1-about 49 atomic %.

The diffusion barrier may prevent or retard the effect of thermalstability of the Ag-based reflection layer and an ohmic contactcharacteristic caused by a material of another layer excluding thereflection layer diffused toward the reflection layer. As a result, thediffusion barrier may prevent or retard voids from being formed at aninterface between a nitride-based semiconductor layer and the Ag-basedreflection layer and may prevent or retard surface agglomeration fromoccurring. The APL may be formed of Al or an Al-based alloy so as toprevent or retard agglomeration of the reflection layer. The Al-basedalloy may include at least one element selected from the solute-elementgroup consisting of Ag, Rh, Cu, Pd, Ni, Ru, Ir, and Pt.

According to example embodiments, a multiple reflection layer electrodemay further include an oxidation protecting layer formed on the APL soas to prevent or retard oxidation of the APL. A difference in surfaceenergy between the material of the diffusion barrier and the material ofthe p-type semiconductor layer may be smaller than a difference insurface energy between the material of the reflection layer and thematerial of the p-type semiconductor layer. The oxidation protectinglayer may be formed of at least one material selected from the groupconsisting of Au, Rh, Pd, Cu, Ni, Ru, Ir, and Pt. The oxidationprotecting layer may be formed in a single layer or multiple layerstructure.

According to example embodiments, a compound semiconductor lightemitting device may include an n-type electrode, an n-type semiconductorlayer, an active layer, a p-type semiconductor layer; and a p-typeelectrode, wherein the p-type electrode is the multiple reflection layerelectrode of example embodiments.

According to example embodiments, a method of fabricating a multiplereflection layer electrode may include forming a reflection layer on ap-type semiconductor layer, forming an APL (agglomeration protectinglayer) on the reflection layer so as to retard agglomeration of thereflection layer, and forming a diffusion barrier between the reflectionlayer and the APL so as to retard diffusion of the APL.

The method may further include forming an oxidation protecting layer onthe APL so as to retard oxidation of the APL. Forming the reflectionlayer may include forming one material selected from the groupconsisting of Ag, an Ag-based alloy, and an Ag-based oxide. The Ag-basedalloy may include at least one element selected from the solute-elementgroup consisting of Al, Rh, Cu, Pd, Ni, Ru, Ir, and Pt. Forming thediffusion barrier may include forming a transparent conductive material.The transparent conductive material may include at least one materialselected from the group consisting of Ti—N, Mo—O, Ru—O, Ir—O, and In—O.Forming the APL may include forming an Al or an Al-based alloy. TheAl-based alloy may include at least one element selected from thesolute-element group consisting of Ag, Rh, Cu, Pd, Ni, Ru, Ir, and Pt.Forming the oxidation protecting layer may include forming at least onematerial selected from the group consisting of Au, Rh, Pd, Cu, Ni, Ru,Ir, and Pt.

The method may further include forming a contact electrode layer betweenthe p-type semiconductor layer and the reflection layer and reducing acontact resistance between the p-type semiconductor layer and thereflection layer. Forming the contact electrode layer may includeforming at least one material selected from the group consisting of aLa-based alloy, an Ni-based alloy, a Zn-based alloy, a Cu-based alloy, athermoelectric oxide, a doped In oxide, ITO, and ZnO.

According to example embodiments, a method of fabricating a compoundsemiconductor light emitting device may include forming an n-typenitride semiconductor layer, an active layer, and the p-type nitridesemiconductor layer on a substrate, forming an n-type electrode on oneside of the n-type nitride semiconductor layer, and forming a p-typeelectrode on the p-type nitride semiconductor layer, wherein the p-typeelectrode is the multiple reflection layer electrode of exampleembodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings. FIGS. 1-6 represent non-limiting, example embodiments asdescribed herein.

FIG. 1 is a schematic cross-sectional view of a structure of aconventional compound semiconductor light emitting device;

FIG. 2 is a photograph showing a surface of the compound semiconductorLED of FIG. 1 on which a p-type electrode is annealed;

FIG. 3 is a scanning electronic microscope (SEM) cross-sectional photoshowing agglomeration of the annealed p-type electrode and voids formedin the p-type electrode as a result of agglomeration;

FIG. 4 is a cross-sectional view of a structure of a multiple reflectionlayer electrode according to example embodiments;

FIG. 5 is a cross-sectional view of a structure of a multiple reflectionlayer electrode according to example embodiments; and

FIG. 6 is a schematic cross-sectional view of a compound semiconductorlight emitting device having a multiple reflection layer electrodeaccording to example embodiments.

It should be noted that these Figures are intended to illustrate thegeneral characteristics of methods, structure and/or materials utilizedin certain example embodiments and to supplement the written descriptionprovided below. These drawings are not, however, to scale and may notprecisely reflect the precise structural or performance characteristicsof any given embodiment, and should not be interpreted as defining orlimiting the range of values or properties encompassed by exampleembodiments. In particular, the relative thicknesses and positioning ofmolecules, layers, regions and/or structural elements may be reduced orexaggerated for clarity. The use of similar or identical referencenumbers in the various drawings is intended to indicate the presence ofa similar or identical element or feature.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Example embodiments will now be described more fully with reference tothe attached drawings, in which example embodiments are shown. Exampleembodiments may, however, be embodied in many different forms and shouldnot be construed as being limited to the embodiments set forth herein.Rather, these embodiments are provided so that this disclosure will bethorough and complete, and will fully convey the scope of exampleembodiments to those skilled in the art. In the drawings, thethicknesses of layers and regions are exaggerated for clarity. Likenumbers refer to like elements throughout the specification.

It will be understood that when an element or layer is referred to asbeing “on”, “connected to” or “coupled to” another element or layer, itcan be directly on, connected or coupled to the other element or layeror intervening elements or layers may be present. In contrast, when anelement is referred to as being “directly on,” “directly connected to”or “directly coupled to” another element or layer, there are nointervening elements or layers present. Like numbers refer to likeelements throughout. As used herein, the term “and/or” includes any andall combinations of one or more of the associated listed items.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various elements, components, regions,layers and/or sections, these elements, components, regions, layersand/or sections should not be limited by these terms. These terms areonly used to distinguish one element, component, region, layer orsection from another region, layer or section. Thus, a first element,component, region, layer or section discussed below could be termed asecond element, component, region, layer or section without departingfrom the teachings of example embodiments.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof.

Example embodiments are described herein with reference tocross-sectional illustrations that are schematic illustrations ofidealized embodiments (and intermediate structures) of exampleembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, example embodiments should not be construed aslimited to the particular shapes of regions illustrated herein but areto include deviations in shapes that result, for example, frommanufacturing. For example, an implanted region illustrated as arectangle will, typically, have rounded or curved features and/or agradient of implant concentration at its edges rather than a binarychange from implanted to non-implanted region. Likewise, a buried regionformed by implantation may result in some implantation in the regionbetween the buried region and the surface through which the implantationtakes place. Thus, the regions illustrated in the figures are schematicin nature and their shapes are not intended to illustrate the actualshape of a region of a device and are not intended to limit the scope ofexample embodiments.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which example embodiments belong. Itwill be further understood that terms, such as those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

FIG. 4 is a cross-sectional view of a structure of a multiple reflectionlayer electrode (a p-type electrode) according to example embodiments.Referring to FIG. 4, a multiple reflection layer electrode 130,according to example embodiments, may include a reflection layer 122, adiffusion barrier 124, and an agglomeration protecting layer (APL) 126,which are sequentially stacked on a p-type nitride semiconductor layer100.

The reflection layer 122 may be formed of a material having an improvedlight reflection characteristic and may reflect light incident on thereflection layer 122. The reflection layer 122 may be formed of silver(Ag), an Ag-based alloy and/or an Ag-based oxide in the form of Ag—O.The Ag-based alloy may include at least one element selected from thesolute-element group consisting of aluminum (Al), rhodium (Rh), copper(Cu), palladium (Pd), nickel (Ni), ruthenium (Ru), iridium (Ir), andplatinum (Pt). In order to reduce a contact resistance between thep-type nitride semiconductor layer 100 and the reflection layer 122, thereflection layer 122 may be a reflective ohmic contact layer having bothlight reflection characteristics and ohmic contact characteristics.

The APL 126 may prevent or retard agglomeration of the reflection layer122. The APL 126 may be formed of Al and/or an Al-based alloy. TheAl-based alloy may include at least one element selected from thesolute-element group consisting of Ag, Rh, Cu, Pd, Ni, Ru, Ir, and Pt.The diffusion barrier 124 may be interposed between the reflection layer122 and the APL 126 and may prevent or retard a material used in formingthe APL 126 from being diffused toward the reflection layer 122. Thediffusion barrier 124 may be formed of a transparent conductivematerial. The transparent conductive material may include at least onematerial selected from the group consisting of a titanium nitride(Ti—N), a molybdenum oxide (Mo—O), a ruthenium oxide (Ru—O), an iridiumoxide (Ir—O), and an indium oxide (In—O). The In—O may further includeat least one dopant selected from the group consisting of tin (Sn), zinc(Zn), gallium (Ga), copper (Cu), and magnesium (Mg). The content of thedopant added to the In—O may be about 0.1-about 49 atomic % so that anohmic contact characteristic of the diffusion barrier 124 may beimproved.

In FIG. 4, each of the reflection layer 122, the diffusion barrier 124,and the APL 126 may be formed to a thickness of about 1 nm-about 1000nm. When the thickness of the APL 126 is larger, an electricalresistance may be increased. When the thickness of the APL 126 issmaller, an agglomeration protecting effect may be reduced and thethickness of the APL 126 may be properly adjusted. The thickness of theAPL 126 may be determined in consideration of the size of the entiresemiconductor device and the thickness of the reflection layer 122. Forexample, the thickness of the reflection layer 122 may range from about50 nm to about 1000 nm, e.g., about 200 nm. When the thickness of thereflection layer 122 is about 200 nm, the thickness of the APL 126 maybe within about 1 nm-about 200 nm. For example, the thickness of the APL126 may be about 100 nm-about 200 nm. The thickness of the diffusionbarrier 124 may be about 50 nm-about 100 nm.

After the reflection layer 122, the diffusion barrier 124, and the APL126 may be sequentially deposited, the stack resultant structure may beannealed at about 300° C.-about 600° C. Respective material layers maybe formed using vapor deposition that is generally used in asemiconductor manufacturing process, for example, chemical vapordeposition (CVD), metal-organic chemical vapor deposition (MOCVD) and/orphysical vapor deposition (PVD), or using an e-beam evaporator.

Characteristics of the multiple reflection layer electrode (p-typeelectrode) illustrated in FIG. 4 will now be described in greaterdetail. Because the surface energy of the material of the reflectionlayer 122, e.g., Ag, an Ag-based alloy and/or an Ag-based oxide in theform of Ag—O, is different from the surface energy of a material of thep-type nitride semiconductor layer 100, agglomeration may occur duringannealing after the reflection layer 122 is stacked. In FIG. 4, in orderto prevent or retard agglomeration, the APL 126, formed of a conductivematerial, whose surface energy difference between the surface energy ofthe material of the p-type nitride semiconductor layer 100 is relativelysmall, for example, Al or an Al-based alloy, may be stacked on thereflection layer 122. The Al-based alloy may include at least onematerial selected from the solute-metal group consisting of Ag, Rh, Cu,Pd, Ni, Ru, Ir, and Pt.

Because these selected materials have a relatively small surface energydifference between the surface energy of the material of the p-typenitride semiconductor layer 100 and also have improved electricalconductivity, the materials may be stacked on the reflection layer 122,may perform an agglomeration protecting function and may serve as anelectrode. In a stacking method of the APL 126, a metal vapor of areflection layer material, generated by an e-beam using a general e-beamevaporator and a metal vapor of an agglomeration protecting layermaterial, may be sequentially exposed to a substrate and therefore maybe stacked in a multiple thin film structure. Annealing may be performedat about 300° C.-about 600° C. for about 5 minutes.

Annealing may be performed in an atmosphere including at least oxygen.Annealing time and atmosphere may not be as important in exampleembodiments, but annealing may be performed for about 30 minutes ormore. When the APL 126 is stacked on the reflection layer 122, adifference between the surface energy of the material of the APL 126 andthe surface energy of the material of the p-type nitride semiconductorlayer 100 may be relatively small. Thus, deformation, which may occurduring subsequent annealing, may be generated similarly in the APL 126and the p-type nitride semiconductor layer 100. Thus, the APL 126 mayprevent or retard the reflection layer 122 from being agglomeratedduring annealing so that the surface of the reflection layer 122 may bekept in a flat state. However, on the other hand, when the APL 126 isstacked on the reflection layer 122 and is annealed, a portion of thematerial used in forming the APL 126 may be diffused toward thereflection layer 122 and thermal stability and ohmic contactcharacteristic of the Ag-based reflection layer 122 may be adverselyaffected.

Thus, a layer, which prevents or retards diffusion between the APL 126and the reflection layer 122 without disturbing the function of the APL126, may be needed. Thus, in order to meet this requirement, thediffusion barrier 124 may be additionally interposed between thereflection layer 122 and the APL 126, as illustrated in FIG. 4. As such,thermal stability and ohmic contact characteristic of the reflectionlayer 122 may be improved compared to the related art. In addition, thediffusion barrier 124 may prevent or retard voids from being formed atan interface between the p-type nitride semiconductor layer 100 and theAg-based reflection layer 122 and may also prevent or retard surfaceagglomeration from occurring.

If agglomeration of the reflection layer 122 and impurity materialdiffusion from another electrode layer to the reflection layer 122 areprevented or retarded, reflectivity of the reflection layer 122 may notbe lowered and a high-reflection state may be maintained. Because thesemiconductor light emitting device having the multiple reflection layerelectrode 130 manufactured according to FIG. 4 may have reducedreflectivity, improvement in light output characteristic may beexpected.

When only the diffusion barrier 124 and the APL 126 are formed on thereflection layer 122, the entire contact resistance of the multiplereflection layer electrode 130 may be increased. Thus, an additionalelectrode, which may reduce a contact resistance, may be interposedbetween the p-type nitride semiconductor layer 100 and the reflectionlayer 122. A contact electrode layer (not shown), which reduces acontact resistance between the p-type semiconductor layer 100 and thereflection layer 122, may be further interposed between the p-typenitride semiconductor layer 100 and the reflection layer 122.

Light generated from the p-type nitride semiconductor light emittingdevice may pass through the contact electrode layer (not shown) and mayreach the reflection layer 122. In addition, because light reflectedfrom the reflection layer 122 may again pass through the contractelectrode layer (not shown), the contact electrode layer (not shown) mayhave increased transparency. Thus, in order to meet this requirement,the contact electrode layer (not shown) may be formed of at least onematerial selected from the group consisting of a La-based alloy, anNi-based alloy, a Zn-based alloy, a Cu-based alloy, a thermoelectricoxide, a doped In oxide, ITO, and ZnO, for example, a Zn—Ni alloy, anNi—Mg alloy, and a Zn—Mg alloy. A doping element of the doped In oxidemay include at least one selected from the group consisting of Mg, Ag,Zn, Sc, Hf, Zr, Te, Se, Ta, W, Nb, Cu, Si, Ni, Co, Mo, Cr, Mn, Hg, Pr,and La.

The contact electrode layer (not shown) may be formed to a thickness ofabout 0.1 nm-about 200 nm. If the thickness of the contact electrodelayer is larger, the entire reflectivity may be lowered, and if thethickness of the contact electrode layer is smaller, a stacking effectmay be lowered. Thus, the thickness of the contact electrode layer maybe properly adjusted. The thickness of the contact electrode layer (notshown) may be determined in consideration of the size of the entiresemiconductor device and the thickness of the reflection layer 122. Forexample, when the thickness of the reflection electrode layer 122 isabout 200 nm, the thickness of the contact electrode layer may be about1 nm-about 200 nm. For example, the thickness of the contact electrodelayer may be about 3 nm. After the contact electrode layer (not shown),the reflection layer 122, the diffusion barrier 124 and the APL 126 aresequentially stacked, the stack resultant structure may be annealed atabout 300° C.-about 600° C.

FIG. 5 is a cross-sectional view of a structure of a multiple reflectionlayer electrode according to example embodiments. Referring to FIG. 5, amultiple reflection layer electrode 140 may include a reflection layer122, a diffusion barrier 124, an agglomeration protecting layer (APL)126, and an oxidation protecting layer 128, which are sequentiallystacked on a p-type nitride semiconductor layer 100. Functions of thereflection layer 122, the diffusion barrier 124, and the APL 126,materials used in forming them, and methods of forming the same havebeen already described and thus, repeated descriptions thereof will beomitted.

When a metal material, e.g., Cu, is used in forming the APL 126, acurrent-voltage characteristic of an electrode may be deteriorated dueto oxidation of the surface of the APL 126. In order to prevent orretard agglomeration that occurs in the reflection layer 122, thediffusion barrier 124 and the APL 126 may be formed on the reflectionlayer 122 and agglomeration on the surface of the reflection layer 122may decrease. However, the surface of the APL 126 may be partiallyoxidized. If the surface of the APL 126 is oxidized, the current-voltagecharacteristic of the electrode may be deteriorated so that an operatingvoltage of a compound semiconductor light emitting device may beincreased.

Such oxidation may cause a problem in mass-production of semiconductorlight emitting devices. In order to suppress surface oxidation of theAPL 126, the oxidation protecting layer 128 may be additionally formedon the APL 126. For example, the oxidation protecting layer 128 may bestacked on the APL 126 and may suppress oxidation of the APL 126. Thus,the oxidation protecting layer 128 may be further formed on the APL 126so that agglomeration of the reflection layer 122 may be suppressed,which is the function of the APL 126. Oxidation of the APL 126 may besuppressed, which is the function of the oxidation protecting layer 128.

The oxidation protecting layer 128 may be formed of at least onematerial selected from the group consisting of Au, Rh, Pd, Cu, Ni, Ru,Ir, and Pt, and the oxidation protecting layer 128 may be formed in asingle layer or multiple layer structure. The oxidation protecting layer128 may be formed to a thickness of about 1 nm-about 1000 nm, forexample, about 20 nm-about 500 nm.

After the reflection layer 122, the diffusion barrier 124, the APL 126,and the oxidation protecting layer 128 may be sequentially stacked onthe p-type nitride semiconductor layer 100, the stack resultantstructure may be annealed at about 300° C.-about 600° C. A contactelectrode layer (not shown), which reduces a contact resistance betweenthe p-type semiconductor layer 100 and the reflection layer 122, may befurther interposed between the p-type nitride semiconductor layer 100and the reflection layer 122. The contact electrode layer (not shown)may be formed to a thickness of about 0.1-about 200 nm. A material usedin forming the contact electrode layer (not shown) has already beendescribed and thus, a detailed description thereof will be omitted.After the contact electrode layer (not shown), the reflection layer 122,the diffusion barrier 124, the APL 126, and the oxidation protectinglayer 128 are sequentially stacked on the p-type nitride semiconductorlayer 100, the stack resultant structure may be annealed at about 300°C.-about 600° C.

FIG. 6 is a schematic cross-sectional view of a compound semiconductorlight emitting device having a multiple reflection layer electrodeaccording to example embodiments. A compound semiconductor lightemitting device 150 having a multiple reflection layer electrode 140 isillustrated in FIG. 6. For example, the compound semiconductor lightemitting device 150 may include an n-type semiconductor layer 112, anactive layer 114, and a p-type semiconductor layer 116, which aresequentially stacked on a substrate 110. The compound semiconductorlight emitting device 150 may further include an n-type electrode 120formed on an etch surface of the n-type semiconductor layer 112 and ap-type electrode 140 formed on the p-type semiconductor layer 116. Themultiple reflection layer electrode 140 illustrated in FIG. 5 may beused as the p-type electrode 140.

The p-type electrode 140 may include a reflection layer 122, a diffusionbarrier 124, an agglomeration protecting layer (APL) 126, and anoxidation protecting layer 128, which are sequentially stacked on thep-type semiconductor layer 116. Detailed structure and description ofthe multiple reflection layer electrode 140 illustrated in FIG. 5 havebeen already described and thus, repeated description thereof will beomitted. The substrate 110 may be one of Si, GaAs, SiC, GaN, andsapphire substrates. The n-type semiconductor layer 112 may be ann-GaN-based Group III-V nitride semiconductor layer, for example, ann-GaN layer or an n-GaN/AlGaN layer. The p-type semiconductor layer 116may be a p-GaN-based Group III-V nitride semiconductor layer, forexample, a p-GaN layer or a p-GaN/AlGaN layer.

The active layer 114 may be a GaN-based Group III-V nitridesemiconductor layer, which is formed of In_(x)Al_(y)Ga_(1-x-y)N (about0≦x≦1, about 0≦y≦1 and about 0≦x+y≦1), for example, an InGaN layer or anAlGaN layer. The active layer 114 may have one of a multiple quantumwell (MQW) and a single quantum well, and the structure of the activelayer 114 may not restrict the technical scope of example embodiments.For example, the active layer 114 may be formed in a GaN/InGaN/GaN MQWor GaN/AlGaN/GaN MQW structure.

In the structure of the compound semiconductor light emitting deviceaccording to example embodiments, if forward voltages are appliedbetween the n-type electrode 120 and the p-type electrode 140, electronsin a conduction band of the active layer 114 may be recombined withholes in a valence band and light may be emitted from the active layer114 due to energy corresponding to a band gap, which is the energydifference between the valance band and the conduction band. Lightemitted from the active layer 114 may be reflected by the p-typeelectrode 140 and may be emitted to the outside of the semiconductorlight emitting device 150 through the substrate 110.

In the compound semiconductor light emitting device according to exampleembodiments, the n-type electrode 120 may be formed of a metal material,e.g., Al, Ag, Au and/or Pd. In addition, a multiple reflection layerelectrode, according to example embodiments, may be used as the n-typeelectrode 120. In other words, the n-type electrode 120 may include areflection layer 122, a diffusion barrier 124, an APL 126, and anoxidation protecting layer 128, which are sequentially stacked on then-type semiconductor layer 112. Because the compound semiconductor lightemitting device having the multiple reflection layer electrode 140according to example embodiments has reduced reflectivity, improvementin light output characteristics may be expected.

According to example embodiments, a multiple reflection layer electrodehaving improved thermal stability and ohmic contact characteristic and acompound semiconductor light emitting device having the same may beobtained. According to example embodiments, a diffusion barrier and anagglomeration protecting layer (APL) may be used such that agglomerationmay be prevented or retarded from occurring on the surface of areflection layer. For example, the diffusion barrier may prevent orretard a material excluding the reflection layer from being diffusedtoward the reflection layer such that thermal stability and ohmiccontact characteristic of the reflection layer may be improved.

In addition, an oxidation protecting layer may be stacked on the APLsuch that oxidation of the APL may be prevented or retarded. Thus,according to example embodiments, an electrode for a semiconductor lightemitting device having a relatively low electrical resistance may beobtained and a semiconductor light emitting device having relativelysmall power consumption may be obtained. In addition, according toexample embodiments, stable mass-production of semiconductor lightemitting devices may be possible.

While example embodiments have been particularly shown and describedwith reference to example embodiments thereof, it will be understood bythose of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the following claims.

1. A multiple reflection layer electrode comprising: a reflection layeron a p-type semiconductor layer; an APL (agglomeration protecting layer)on the reflection layer so as to retard agglomeration of the reflectionlayer; and a diffusion barrier between the reflection layer and the APLso as to retard diffusion of the APL; a contact electrode layer betweenthe p-type semiconductor layer and the reflection layer and reducing acontact resistance between the p-type semiconductor layer and thereflection layer.
 2. The multiple reflection layer electrode of claim 1,further comprising: an oxidation protecting layer formed on the APL soas to retard oxidation of the APL.
 3. The multiple reflection layerelectrode of claim 2, wherein the oxidation protecting layer is formedof at least one material selected from the group consisting of Au, Rh,Pd, Cu, Ni, Ru, Ir, and Pt.
 4. The multiple reflection layer electrodeof claim 3, wherein the oxidation protecting layer is formed in a singlelayer or multiple layer structure.
 5. The multiple reflection layerelectrode of claim 2, wherein a thickness of the oxidation protectinglayer is about 1 nm-about 1000 nm.
 6. The multiple reflection layerelectrode of claim 2, wherein a stack resultant structure composed ofthe reflection layer, the diffusion barrier, the APL, and the oxidationprotecting layer is annealed at about 300° C.-about 600° C.
 7. Themultiple reflection layer electrode of claim 1, wherein the reflectionlayer is a reflective ohmic contact layer.
 8. The multiple reflectionlayer electrode of claim 1, wherein the reflection layer is formed ofone material selected from the group consisting of Ag, an Ag-basedalloy, and an Ag-based oxide.
 9. The multiple reflection layer electrodeof claim 8, wherein the Ag-based alloy includes at least one elementselected from the solute-element group consisting of Al, Rh, Cu, Pd, Ni,Ru, Ir, and Pt.
 10. The multiple reflection layer electrode of claim 1,wherein the diffusion barrier is formed of a transparent conductivematerial.
 11. The multiple reflection layer electrode of claim 10,wherein the transparent conductive material includes at least onematerial selected from the group consisting of Ti—N, Mo—O, Ru—O, Ir—O,and In—O.
 12. The multiple reflection layer electrode of claim 11,wherein the In—O further includes at least one dopant selected from thegroup consisting of Sn, Zn, Ga, Cu, and Mg.
 13. The multiple reflectionlayer electrode of claim 12, wherein a content of a dopant added to theIn—O is about 0.1-about 49 atomic %.
 14. The multiple reflection layerelectrode of claim 1, wherein the APL is formed of Al or an Al-basedalloy.
 15. The multiple reflection layer electrode of claim 14, whereinthe Al-based alloy includes at least one element selected from thesolute-element group consisting of Ag, Rh, Cu, Pd, Ni, Ru, Ir, and Pt.16. The multiple reflection layer electrode of claim 1, wherein thecontact electrode layer is formed of at least one material selected fromthe group consisting of a La-based alloy, an Ni-based alloy, a Zn-basedalloy, a Cu-based alloy, a thermoelectric oxide, a doped In oxide, ITO,and ZnO.
 17. The multiple reflection layer electrode of claim 16,wherein a doping element in the doped In oxide includes at least oneselected from the group consisting of Mg, Ag, Zn, Sc, Hf, Zr, Te, Se,Ta, W, Nb, Cu, Si, Ni, Co, Mo, Cr, Mn, Hg, Pr, and La.
 18. The multiplereflection layer electrode of claim 16, wherein a thickness of thecontact electrode layer is about 0.1 nm-about 200 nm.
 19. The multiplereflection layer electrode of claim 16, wherein a stack resultantstructure composed of the contact electrode layer, the reflection layer,the diffusion barrier, the APL, and the oxidation protecting layer isannealed at about 300° C.-about 600° C.
 20. The multiple reflectionlayer electrode of claim 1, wherein a thickness of each of thereflection layer, the diffusion barrier, and the APL is about 1 nm-about1000 nm.
 21. The multiple reflection layer electrode of claim 1, whereina stack resultant structure composed of the reflection layer, thediffusion barrier, and the APL is annealed at about 300° C.-about 600°C.
 22. A compound semiconductor light emitting device comprising: ann-type electrode; an n-type semiconductor layer; an active layer; ap-type semiconductor layer; and a p-type electrode, wherein the p-typeelectrode is the multiple reflection layer electrode of claim 1.